Method for the detection and classification of defects in internal combustion engines

ABSTRACT

The present invention relates to a method for detecting and classifying cylinder defects in internal combustion engines, and more specifically to a method for classifying such defects into a) fuel system and b) compression defects.

United States Patent Scott [451 July 18, 1972 METHOD FOR THE DETECTIONAND References Cited CLASSIFICATION OF DEFECTS IN UNITED ST ATES PATENTSINTERNAL COMBUSTION ENGINES 3,421,367 1/1969 Mears et a1. ..73/116 l 721lnvenm will! RYa| 2,675,701 4/1954 Bidwell ..73/141 A [73] Assignee: TheUnited States of America 8 represented by the Secretary of the ArmyPrimary Examiner-Jerry W. Myracle [22] File? m 20 1970 Attorney-Harry M.Saragovitz, Edward J. Kelly, Herbert Berl and R. M. Lyon [21] Appl. No.:82,378

ABSTRACT 2% g: The present invention relates to a method for detectingand E Field Search 73/116 136 117 3 classifying cylinder defects ininternal combustion engines, and more specifically to a method forclassifying such defects into a) fuel system and b) compression defects.

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ATTORNEYS METHOD FOR THE DETECTION AND CLASSIFICATION OF DEFECTS ININTERNAL COMBUSTION ENGINES The invention described herein may bemanufactured, used,

and licensed by or for the Government for governmental purposes withoutpayment to me of any royalty thereon.

BACKGROUND OF THE INVENTION 1. Field of the Invention Based on theprinciple that variations in power output resulting from correspondingvariations in the instanteous speed of an engine are directly related tosubstandard power strokes, the instant invention provides a method fordetecting cylinder defects in internal combustion engines andclassifying them into: a. fuel system and b. compression defects. Morespecifically the method comprises the steps of: (a) measuring the cyclictorque variation of an internal combustion engine in the operating mode;(b) measuring the cyclic torque variation of the same engine in thedriven mode; and (c) comparing the results of the two measuring steps todetermine whether the cause of the defect detected thereby is relatedto: (l) a fuel system problem, in which case the defect will occur onlyduring the measurement of step a; or (2) is a compression problem, inwhich case the defect will appear in the measurements of step b. orsteps b. and a.

2. Description of the Prior Art In the prior art, detection of cylinderdefects has been accomplished largely through the use of dynamometersattached to the wheels of the vehicle, which instruments were capable ofdetecting variation in the total output of the engine in the drivingmode. All this has supplied useful information regarding the conditionof the engine. However, no known rapid method exists for classifying thedefect into either a fuel system or an individual cylinder orcompression defect so that the rapairmans search for the problem area orcomponent is quite necessarily broad and unnecessarily quitecomplicated.

It is therefore an object of the present invention to provide a methodfor simplifying the repairmans search for such defects by supplying arelatively simplified method by which such cylinder defects are not onlyeasily detected but are simultaneously classified into either fuelsystem or compression defects.

SUMMARY OF THE INVENTION The instant invention proposes the evaluationof cyclic rotational torque variation of a dead engine which is powerrotated in combination with the evaluation of observations of the cyclicpower variation of the same engine under operating conditions. If theengine does indicate abnormal cyclic power variations under power, thesource of the problem can be determined by separating the evaluationinto a (1) fuel system or 2) compression problem by rotating the dead"engine using some second driving means and observing any cyclicrotational torque pattern generated in this mode. When the dead" enginetests indicate cyclic variation, this is an indication of a compressionproblem. If no unusual cyclic variation occurs when the dead engine isrotated, this indicates that the problem of unusual cyclic powervariation detected under the driving mode is due to an injector or fuelproblem. If the measure of power level is low as indicated by thecalibrated cyclic power test described below, this would indicate eithera compression, turbo-charger or general fuel supply problem. Hence thepresent invention provides cylinder diagnosis as to whether a problem isof the fuel or compression type rather than merely determining that theproblem is a cylinder problem.

Generally, the method is achieved using a cylinder performance monitorconsisting basically of a processing black box 19 (described in slightlymore detail below) which has static input 20 and 21 cyclic static input22 and a timing reference 23 for coherent sensing of engine cylinders.The information from the cyclic dynamic power input 20 and the timingreference 16 is processed, stored or indicated, Operation can beswitched to static input 21 when a fault is apparent and the signal isthen applied to the processing network with timing reference 16 forcomparison with cyclic dynamic power standards to determine if the faultis either in the fuel system or the compression system. The finaldisplay of information can be in any preferred format or applieddirectly to a diagnostic system readout. The invention can also be madeto provide a calibrated output of cyclic dynamic power level which alsocan be processed for diagnostic application.

It should be noted at this point that the equipment and methodsdescribed hereinafter are equally applicable to single as well asmultiple cylinder engines.

The method of the instant invention is based on the principle ofmeasuring and displaying instantaneous variations in engine speed whilethe engine is in the operating and nooperating crank mode.

The power output of a reciprocating engine is, by nature, a series ofspecific impulses recurring cyclically. For a piston engine, each powerstroke produces a discrete impulse. A typical resulting power graphresembles a full wave rectifying voltage wave form shown in FIG. 3.

Failure of any cylinder to fire, or to fire properly, would result in apower curve showing some variation from the standard as shown in FIG. 4.The engine's fly wheel and the momentum of rotating parts can tend tosmooth the curve but, nevertheless, there is a distinct dip in power andin velocity associated with the power stroke of each cylinder which isdelivering less than average power.

On a typical spark ignition engine, it has been found that the pulsesgenerated by the engine alternator vary in frequency directly with thespeed of the engine. To process this frequency variation electroniccircuitry has been implemented in a manner that yields a pulsating DCwaveform. Experimentation on an eight cylinder engine has shown adefinite drop in DC level occurs when deliberate ignition or compressionmalfunctions are introduced. The DC drop down or negative pulse occursjust after the firing stroke of the effected cylinder or cylinders. Onthe spark ignition engine, the alternator is chosen as a velocity sensorbecause of the convenience of monitoring the output. The implementationof this approach, however, can be substituted by using tachometercoupling to engines.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustratingthe present invention.

FIG. 2 is a functional block diagram of the cylinder performance monitorillustrating the concept of the proposed equipment. Solid line block 24define the basic four to six cylinder configuration and the dottedblocks define those basic modules and meters 25 necessary to expand thehardware to accommodate eight to twelve cylinder engines. Subunits toprovide tachometer and/or alternator and generator options are shown assubunits inclosed in dotted line boxes 25.

FIG. 3 shows a typical full wave rectifying voltage wave form.

FIG. 4 illustrates power variations with No. 5 cylinder misfiring.

FIG. 5 represents a tachometer sensor device attached to an engine.

FIG. 6 illustrates the individual cylinder monitoring meters for anormal engine at idle.

FIG. 7 shows the individual cylinder monitoring meter where No. 6cylinder is delivering sub-normal power at idle.

FIG. 8 represents meter presentation during cranking test where No. 6cylinder is in compression.

The major subunits of the cylinder performance monitor necessary toimplement the method of the instant invention are the speed variant DCsignal input processing circuits (i.e., tachometer, alternator, andgenerator), ring counter engine type selector, firing order selector,and an individual meter, analog gates, peak detectors and meter drives.

The input signals for timing are photoelectric diodes operating from alight source controlled by apertures in two metal discs. The cylindercount disc light output will be shaped into narrow pulses properlyamplified to provide the cylinder input to a conventional solid statering counter. The ring counter will be reset on each count reset discpulse by a single pulse indicating two revolutions of the engine. Thering counter and its subsequent timing are easily modified toaccommodate a different number of cylinder engines by insertion of a newdisc and circuit inhibition.

The accelerometer and associated electronics option provides similarreference to the tachometer timing disc which provides proper gating ofsignals for cylinder display.

The output of the DC processing of signals is fed in parallel to theanalog gate circuits. The second input to the individual analog gatesare the timing complex outputs identifying the interval of time duringwhich the cylinder is monitored. Peak detection of individual cylindersis employed to permit greater threshold for integration and smoothermeter presentation.

Expansion of the system can be accomplished to include, for exampleeight or 12 cylinders engine inputs by the addition of additionaltachometer assembly timing discs, added stages in the ring counterselection matrix and individual meter processing chains plus switchesand correct inhibit circuits.

Where engine speed cannot be sensed by the use of a mechanicaltachometer assembly described, alternate signals from accelerometers,alternators, generators or other pick up devices may be provided. Thesesignals must be processed to a form similar to the DC engine speed,engine cycle and cylinder cycle indicator signals derived from atachometer and timing assembly.

In the alternator option a filtered DC signal is amplified and deliveredto a variable single shot followed by filtering in a differentialamplifier. At this point the signal is switched to a common point foramplification, gating, peak detection and displaying for operatorinterpretation.

The generator option is similar to the alternator with the exceptionthat additional filtering must be provided to guard against brush arcingand operation of the regulator.

It is therefore an object of the present invention to provide a methodfor evaluation of the cyclic rotational torque variations of a deadengine which is power rotated in addition to observing the cyclic powervariations under operating conditions.

It is yet another object of my invention to provide cylinder diagnosisas to whether the problem arises in the fuel or compression systemrather than just a cylinder malfunction.

Still further objects and advantages of the present invention willbecome readily apparent to one skilled in the art from the followingdescription of preferred embodiment of the invention and accompanyingdrawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT The monitor bookings to thevehicle must be first fully achieved and then started and run untilsteady idle is achieved. The engine speed should be adjusted to themanufacturers recommended idling speed. Readings can then be made fromthe individual cylinder monitoring meters and from this presentation theoperator can determine which cylinders are low in output. To determinewhether the power loss is due to compression or fuel defects, the engineis then stopped and the fuel flow or ignition is shut off. The engine isthen cranked in a dead condition by any suitable means and anotherreading is made of the meters. If the power loss is due to compression ameter will show an increase in voltage corresponding to the increase inengine speed as the leaking cylinder goes through a compression stroke.Where all meters are showing a normal reading, it can be inferred thatthe observed power loss was due to a fuel system defect and not acompression defect.

A cylinder performance monitor, consisting of a processing block box 19which has inputs 20 and 21, and cyclic static input 22 and timingreference 23 for coherent sensing of engine cylinders. All theinformation from cyclic dynamic power input 20 and timing reference 23is processed, stored or indicated. Operation is switched to static input21 when a fault is apparent and the signal is then applied to theprocessing network with timing reference 23 for comparison with cyclicdynamic power standards to determine if the fault is either in the fuelor compression system.

Tachometer adapter coupling 26 shown in FIG. 5 generally consists ofbevel gear drive sensing 27 coupled to tachometer output connection, notshown here, on the engines and provides a substitute connection fortachometer cable 28 while servicing engines.

The tachometer assembly also shown in FIG. 5 is a standard tachometer 29designed to be mounted on tachometer adapter coupling 26 describedabove. Tachometer 29 used is double ended, that is its shaft extendsfrom both sides of the case. Timing disc 30 containing seven slots 31for a six cylinder engine is mounted on rear tachometer shaft extension32. Six of slots 31 are arranged equally spaced around disc 30. Slots 31are then made to correspond to the power stroke of each cylinder. Aseventh slot located on a different diameter is used to identify thenumber one cylinder firing point. As shown in the drawing, integral lampphoto cell block 32 is mounted on the tachometer to stradle timing disc30. Each revolution in the engine then produces three pulses from photocell 32. Each cycle (2 revolutions) of the engine, not shown, producessix photo cell 32 pulses corresponding to cylinder firings and one pulsecorresponding to the number one cylinder firing. Timing disc 30 isadjustable on shaft 34 to permit synchronization with the crank shaft ofthe engine.

In use vehicle tachometer cable 28 is removed from its connection to theengine. The tachometer adapter described above with its integraltachometer 29 and timing assembly 39 is connected to engine tachometeroutput 35. The vehicle tachometer is then reconnected to the otheroutlet of the adapter and is driven by bevel gear 27. The next step isto crank the engine over until the number one piston is at top deadcenter on its firing stroke. Timing disc 39 on the rear of tachometer 29is then adjusted to line up with a pointer built into the assembly. Oncetiming disc 29 is adjusted the vehicle is started and operated at idlespeed (generally in trucks and other large vehicle engines this isapproximately 600 rpm).

Precise indication of individual cylinder performance can be providedthrough the use of volt meter type arrangement which permits the lowpower cylinders to produce an output which is indicated on the meter asa significantly above average reading. Other types of indicator systemsmay also be used.

The equipment may also contain the necessary outputs to enable the speedwave form described above to be displayed on a cathode ray oscilloscope.Although the interpretation of the ray trace may require some skill onthe part of the operator it is submitted that the ability for visualexamination of the wave forms provides a superior output which can leadto more rapid detection classification and therefore repair of the powersystem.

The principle of engine analyses through an examination of the minutefluctuations in crank shaft speed as reflected in variations in thespeed as produced in the tachometer, is applicable to either dieselengines or spark ignition type engines.

The speed signal is generated by a DC tachometer generator, alternatoror generator which is mechanically driven by the engine as describedabove, i.e., by a belt or gear drive means. The signal is a positive DCvoltage whose average level represents the steady state of the engine. Apositive going change in this level is caused by an increase in thespeed and a negative going change results from a decrease in speed.

When the monitor is operated in the engine idle mode, only negativechanges in the speed signal are processed. These changes are the resultof substandard power being delivered by a cylinder. In the first stageof processing, the raw tachometer signal is low passed filter to thefundamental frequency of the engine being tested. This results inremoving the DC or steady state speed information and enhancing anyspeed variations occurring at the fundamental frequency. If a negativechange in speed is present, it will start during the power stroke of thecylinder affected. The speed decrease will continue into the nextcylinder's power stroke and then slowly the dropping speed will berecovered over the remaining portion of the engine cycle. Thesignificant information is contained in the initial dropping speed whichoccurs during the first power stroke. The remaining speed decrease andeventual recovery are the result of the initial dropping speed. Further,processing is performed so that the significant information (initialspeed decrease) can be extracted and the resulting effect during theremainder of the engine cycle be eliminated in the cranking mode ofoperation. Only positive changes in the speed signal are processed inthe driven (cranking) mode. These changes are the result of lower thanaverage compression developed during the compression stroke whichproduces a speed increase during the low compression stroke. Theprocessing of this signal is performed by the same circuit as that usedfor the idle engine signal, but with an additional inverting amplifierand a low pass filter inserted before the first differentiation stage.The inverting amplifier provides the proper signal polarity and gain forthe processing network. The low pass filter, stays for the lowerfundamental frequency at cranking speed.

Analog switches perform the time correlation of the speed signal. Thisis accomplished by sampling the speed signal at a frequency whichincludes the number of cylinders in the engine being tested. If thereare six cylinders then six samples per engine cycle are obtained by sixanalog switches. Each switch then transmits the output to a cylindermeter for display. The analog switches are triggered by the TDC timingpulses in the firing order. The sampling interval is 1 over n, where nis a cylinder.

I wish it to be understood that I do not desire to be limited to theexact details of construction shown and described, for obviousmodifications will occur to a person skilled in the art.

I claim:

1. A method for detecting cylinder defects in an internal combustionengine and classifying them into fuel system and compression defectscomprising the steps of:

a. measuring the cyclic torque variation of said internal combustionengine in the operating mode;

b. measuring the cyclic torque variation of said internal combustionengine in the driven mode; and

c. comparing the results of said two measuring steps to determinewhether the cause of a defect detected thereby is related to:

a fuel system problem in said internal combustion engine, in which casesaid defect will occur only during the measurement of step a; or

is a compression problem therein, in which case said defect will appearin the measurements of step b.

2. The method as described in claim 1 wherein said measuring of thecyclic torque variation of steps a and b is accomplished by using atachometer sensor comprising:

a. a tachometer adapter coupling designed to couple to said tachometeroutput connection of said internal combustion engine;

b. a permanent mounting of said tachometer (alternator, generator orother pickup device) for measuring cyclic torque.

3. The method as described in claim 1 wherein said engine in step ameasures cyclic torque and is used to provide a calibrated measure ofthe power output capability of said internal combustion engine throughboth positive and negative going changes.

4. The method as described in claim 3 wherein the cylinder of saidinternal combustion engine delivering substandard power is identifiedand evaluated.

5. The method for detecting cylinder defects in an internal combustionengine and classifying them into fuel system and compression defectscomprising the steps of claim 4 wherein relative performance ofdifferent types of fuel injections, piston rings, valves, valve settingand cylinder head geometry are identified and evaluated.

6. The method for detecting cylinder defects in an internal combustionengine and classifying them into fuel system and compression defectscomprising the steps of claim 5 wherein said method is for measuring abalance of power and determines the total calibrated measure which maybe referenced for a family of engines.

7. The method of claim 1 and the additional step of indicating that theydo occur simultaneously when fuel systems and compression defects occurat the same time.

a a a

1. A method for detecting cylinder defects in an internal combustionengine and classifying them into fuel system and compression defectscomprising the steps of: a. measuring the cyclic torque variation ofsaid internal combustion engine in the operating mode; b. measuring thecyclic torque variation of said internal combustion engine in the drivenmode; and c. comparing the results of said two measuring steps todetermine whether the cause of a defect detected thereby is related to:a fuel system problem in said internal combustion engine, in which casesaid defect will occur only during the measurement of step a; or is acompression problem therein, in which case said defect will appear inThe measurements of step b.
 2. The method as described in claim 1wherein said measuring of the cyclic torque variation of steps a and bis accomplished by using a tachometer sensor comprising: a. a tachometeradapter coupling designed to couple to said tachometer output connectionof said internal combustion engine; b. a permanent mounting of saidtachometer (alternator, generator or other pickup device) for measuringcyclic torque.
 3. The method as described in claim 1 wherein said enginein step a measures cyclic torque and is used to provide a calibratedmeasure of the power output capability of said internal combustionengine through both positive and negative going changes.
 4. The methodas described in claim 3 wherein the cylinder of said internal combustionengine delivering substandard power is identified and evaluated.
 5. Themethod for detecting cylinder defects in an internal combustion engineand classifying them into fuel system and compression defects comprisingthe steps of claim 4 wherein relative performance of different types offuel injections, piston rings, valves, valve setting and cylinder headgeometry are identified and evaluated.
 6. The method for detectingcylinder defects in an internal combustion engine and classifying theminto fuel system and compression defects comprising the steps of claim 5wherein said method is for measuring a balance of power and determinesthe total calibrated measure which may be referenced for a family ofengines.
 7. The method of claim 1 and the additional step of indicatingthat they do occur simultaneously when fuel systems and compressiondefects occur at the same time.